The increasing usage of chemical salts as melting agents in combination with sand to promote traction upon winter roads causes increased damage to the metal undercarriage of vehicles using the roads. The splashing of surface water containing salts results in a chemical reaction between the metal undercarriage and the particular chemicals involved. A common road treating chemical such as calcium chloride in the presence of water can form a dilute hydrochloric acid substance which attacks the metal on contact.
The application of protective coating compositions such as that described, for example in U.S. Pat. No. 3,313,635 delays the deterioration process to a certain extent but is not completely effective. The use of sand with the salt material causes the protective coating composition to become mechanically abraded to such an extent that the salt-containing liquid permeates through to the metal. In some instances, particularly when the vehicles are stored in overnight heated garages, severe metal erosion exists under an otherwise intact coating of undercoat material. The liquid diffuses through the undercoat carrying the corrosive salts in solution for reacting at the temperatures provided within the heated garage enclosure. Removing intact layers of undercoat material reveals badly eroded metal substrates which remain undetected until holes appear in the opposite metal surface.
The erosion of the metal undercarriages is especially severe in northern regions of the United States where hundreds of thousands of tons of salt and sand are applied in the course of a particularly severe winter season. Otherwise operable vehicles are discarded in most instances since the rusting is not discovered until such a state of deterioration has occurred that replacement and repair becomes prohibitively expensive.
The purpose of this invention is to provide methods and materials for providing long-term protection to metal surfaces exposed to heavy concentrations of acid materials.